DUAL FUNCTIONS OF WINGLESS IN THE DROSOPHILA LEG IMAGINAL DISC

The Drosophila gene wingless is a member of the Wnt gene family, a gro up of genes that are involved in embryonic development and the regulat ion of cell proliferation. wingless encodes a secreted glycoprotein th at plays a role in embryogenesis as well as in the development of adul t structures. In the primordia of the adult limbs, the imaginal discs, wingless is expressed in an anterior ventral sector and is required f or specification of ventral fate. Ectopic expression of low levels of Wingless in the leg discs leads to partial ventralization and outgrowt hs of the proximodistal axis. Wingless has thus been proposed to speci fy ventral fate in a concentration dependent manner (i.e., as a morpho gen) and to organize the proximodistal axis. We have extended the anal ysis of Wingless function in the leg primordium through targeted ectop ic expression. We find that Wingless has two functions in the leg disc . In the specification of ventral fate, our data indicate that Wingles s does not function as a morphogen but instead appears to collaborate with other factors. In addition to its role in ventral fate specificat ion, Wingless inhibits the commitment of dorsal cells toward a determi ned state and influences the regulation of proliferation. We propose a model in which Wingless achieves separate functions via spatially reg ulated mechanisms and discuss the significance of these functions duri ng axial patterning and organization.